Field of the Invention
[0001] The present invention relates to a wind turbine blade assembly comprising a wind
turbine blade and an aeroshell extender piece. The invention further relates to an
associated method of manufacture.
Background of the Invention
[0002] Aerodynamic shells, also called aeroshells or fairings, can be used in an effort
to present a more aerodynamic airfoil profile for sections of wind turbine blades.
International Patent Application Publication
WO 2013/092852 shows a wind turbine blade assembly wherein a blade part is mounted on a cylindrical
blade extender part, with an aeroshell used to effectively convert the cylindrical
extender into a blade portion having an airfoil profile.
[0003] However, while the use of such aeroshells can improve aerodynamic performance of
a wind turbine blade section, they can also introduce additional complications with
regard to the distribution of stresses and strains in the general wind turbine blade
structure. In particular, the extended trailing edge formed by the end of the aeroshell
section is regularly subjected to relatively high stress levels during wind turbine
operation. Accordingly, increased levels of reinforcement material are required to
prevent failure of the aeroshell, which increases the eventual weight and cost of
wind turbine blades utilising such aeroshells.
[0004] WO 2011/157849 discloses a blade provided with a pre-manufactured trailing edge part for an outboard
part of the blade. In one embodiment, the pre-manufactured part is provided with channels
formed in the surface of the part having a depth of 0 to 10 mm with the purpose of
minimising noise.
[0005] EP 1 338 793 discloses a blade provided with trailing edge serrations at an outboard part of the
blade in order to minimise noise emissions.
[0006] WO 2010/043647 discloses a blade provided with a number of trailing edge sections, such as trailing
edge flaps, along an outboard part of the blade, and which are individually controllable.
[0007] It is an object of the invention to provide an aeroshell construction which is relatively
flexible, and which is arranged to better withstand operational stresses and strains
when installed as part of a wind turbine blade construction.
[0008] Document
US2012/134836, which is seen as the closest prior art, shows a wind turbine blade according to
the preamble of claim 1.
Summary of the Invention
[0009] Accordingly, there is provided a wind turbine blade assembly comprising a wind turbine
blade having a tip end and a root end, and a leading edge and a trailing edge with
a chord length extending therebetween,
wherein the wind turbine blade assembly further comprises an aeroshell extender piece
comprising:
a body for attachment to a trailing edge side of a profile of the wind turbine blade,
the body having a first end for attachment to the trailing edge side of the profile,
and a second trailing edge end to form an extended airfoil trailing edge profile for
a portion of the profile of the wind turbine blade, wherein
the aeroshell extender piece is attached to the wind turbine blade at least partly
using at least one profile wedge, said at least one profile wedge is shaped to compensate
for the geometry of the wind turbine blade.
[0010] By "compensate for the geometry" is meant that the profile wedge locally changes
the geometry of the blade so as to provide a better attachment surface for the body
of aeroshell extender piece. Thereby strains or loads on the connection between the
aeroshell extender piece and the wind turbine blade may be reduced.
[0011] The profile wedges are preferably provided as longitudinally extending pieces having
a substantially wedge shaped cross-section.
[0012] The profile wedge is advantageously arranged between the aeroshell extender piece
and the wind turbine blade, such that it is tapered in direction towards the leading
edge of the blade. Thus, the profile wedge changes the attachment surface to a lower
angle compared to an attachment directly on the wind turbine, which in turn provides
a simple method of lower strain or loads on the connection.
[0013] According to the invention, the aeroshell extender piece is attached to the wind
turbine blade via two profile wedges.
[0014] According to the invention, the profile wedge comprises an inner attachment surface
for attachment to the surface of wind turbine blade and an outer surface for attachment
to the aeroshell extender.
[0015] In a first advantageous embodiment, the inner attachment surface has a first radius
of curvature and the outer attachment surface has a second radius of curvature, wherein
the first radius of curvature is smaller than the second radius of curvature. Accordingly,
the profile wedge provides a more even surface for the attachment, which in particular
for glue bonds lowers strain or loads on the connection.
[0016] According to the invention, the outer attachment surface has a larger surface than
the inner attachment surface. Thus, the profile wedge increase the bond surface, which
in turn provides a stronger glue bond between the aeroshell extender piece and the
wind turbine blade.
[0017] In a third advantageous embodiment, the outer attachment surface is substantially
planar or flat.
[0018] According to the invention, the inboard part or portion of the blade has a substantially
cylindrical part, e.g. having a circular, elliptical or oval cross-section. The inboard
part or portion of the blade is formed as a load-carrying structure of the blade,
and may further advantageously be formed as a blade extender, e.g. for a assembled
blade having an inboard extender part and an outboard blade part.
[0019] The inboard part or portion of the blade advantageously extends along less than 40%
and preferably less than 35% of the total length of the blade. Accordingly, the extender
piece is adapted to be arranged within the inner 40% or 35% of the blade as seen from
a root end of the blade.
[0020] In one advantageous embodiment, the inboard part is a blade extender.
[0021] In another advantageous embodiment, the profile wedge is integrally formed with the
wind turbine blade.
[0022] The profile wedge is advantageously formed as a composite structure, e.g. a core
material, such as balsawood or foamed polymer wrapped in a fibre reinforcement skin.
[0023] In one embodiment, the body comprises a plurality of slits extending from said second
trailing edge end to a point located towards said first end.
[0024] According to the invention, the aeroshell extender piece is preferably adapted to
be fitted to an inboard portion of a profile of a wind turbine blade.
[0025] The inboard part or portion of the blade has a substantially cylindrical part, e.g.
having a circular, elliptical or oval cross-section. The inboard part or portion of
the blade is formed as a load-carrying structure of the blade, and may further advantageously
be formed as a blade extender, e.g. for an assembled blade having an inboard extender
part and an outboard blade part.
[0026] Providing a slitted or slotted extender piece allows for a degree of flexibility
in the structure of the extender piece, reducing the level of strain which is experienced
along the trailing edge end of the extender piece. It will be understood that the
extender piece comprises an aeroshell or fairing, used to provide for an improved
aerodynamic profile of a portion of a wind turbine blade.
[0027] Preferably, said plurality of slits are formed wherein the dimensions of said slits
do not significantly impact aerodynamics in area of extender piece. The slits are
arranged to be aerodynamically insignificant for the normal operation of the wind
turbine blade. It will be understood that aerodynamically insignificant is held to
mean that the dimensions of the slits are small relative to what would be required
to affect the aerodynamic performance of the wind turbine blade profile, e.g. in respect
of noise, lift/drag, etc.
[0028] The extender piece may advantageously be provided as a uniform structure. The extender
piece may further be provided as a passive device, i.e. as a structure without active
parts for controlling the aerodynamic shape of the blade.
[0029] The inboard part or portion of the blade advantageously extends along less than 40%
and preferably less than 35% of the total length of the blade. Accordingly, the extender
piece is adapted to be arranged within the inner 40% or 35% of the blade as seen from
a root end of the blade.
[0030] In a first aspect, the width of each slit is less than the boundary layer height
in the area of the slit. In a second aspect, the width of each slit is less than the
height of the laminar sublayer in the area of the slit.
[0031] Preferably, the plurality of slits define a gap between opposed edges of the slits,
wherein the width of said gap is less than 50 mm, further preferably less than 25
mm. In one embodiment, the slits have a gap width of approximately 15mm.
[0032] Additionally or alternatively, the aeroshell extender piece comprises a flexible
material which is provided in or over the gaps defined by said plurality of slits.
The flexible material may comprise any suitable material which is operable to cover
or seal the gaps without significantly affecting the structural properties of the
aeroshell extender piece, e.g. rubber, a flexible plastics material, canvas, etc.
[0033] Additionally or alternatively, the aeroshell extender piece comprises brushes or
bristles provided at the gaps defined by said plurality of slits. The use of bristles
or brushes at the slits can act to cover the gaps defined by the slits, and reduce
any negative aerodynamic effects which may result by the presence of the slits at
the trailing edge.
[0034] Preferably, said plurality of slits are formed along at least 50% of the depth or
chordwise length of the body of the aeroshell extender piece from said trailing edge
end towards said first end, preferably between 50-90% of the depth of the body from
said trailing edge end towards said first end, preferably approximately 80% of the
depth of the body from said trailing edge end towards said first end.
[0035] According to the invention, the aeroshell extender piece comprises a pressure-side
panel to form a pressure side of the extended airfoil trailing edge profile and a
suction-side panel to form a suction side of an extended airfoil trailing edge profile,
wherein the aeroshell extender piece may further comprise reinforcing elements located
internally of the body of the extender piece, preferably extending between said pressure-
and suction-side panels.
[0036] It will be understood that the aeroshell extender piece may comprise a pressure-side
panel having a relatively concave external surface, to form a section of an external
pressure-side surface of a trailing edge profile. Additionally or alternatively, it
will be understood that the aeroshell extender piece may comprise a suction-side panel
having a relatively convex external surface, to form a section of an external suction-side
surface of a trailing edge profile.
[0037] Preferably, said reinforcing elements comprise bulkhead panels, preferably aligned
with a chordwise direction of the extender piece. It will be understood that apertures
may be provided in said bulkhead panels, e.g. to provide for drainage, pressure equalization,
etc.
[0038] Preferably, the reinforcing elements are arranged wherein a reinforcing element is
positioned adjacent each slit of said plurality of slits, further preferably, the
reinforcing elements are arranged wherein a pair of reinforcing elements are positioned
adjacent the slits of said plurality of slits, the pair of reinforcing elements positioned
either side of the slit.
[0039] By positioning the reinforcing elements or bulkheads either side of the slits, accordingly
the aeroshell extender piece is arranged as a plurality of sections along the length
of the wind turbine blade portion.
[0040] Preferably, said plurality of slits are spaced from each other along the spanwise
length of the extender piece.
[0041] Preferably, said plurality of slits are spaced with approximately 1-5 metres between
adjacent slits, further preferably approximately 2-3 metres between adjacent slits.
[0042] According to the invention, the wind turbine blade comprises an outboard blade part
and an inboard extender part, wherein said aeroshell extender piece is arranged along
a portion of the inboard extender part.
[0043] It will be understood that the outboard blade part may be pitchable relative to the
inboard extender part, e.g. using a blade pitch mechanism provided at the outer end
of the inboard extender part.
[0044] Preferably, the inboard extender part comprises a substantially cylindrical blade
extender.
[0045] By providing an aeroshell extender piece to provide an extended trailing edge of
a cylindrical blade extender, the aerodynamic performance of the inboard blade extender
can be improved.
[0046] According to the invention, the aeroshell extender piece is attached to the wind
turbine blade at least partly using at least one profile wedge, said at least one
profile wedge shaped to compensate for the geometry of the wind turbine blade.
[0047] Preferably, the at least one profile wedge is shaped to provide a substantially planar
bonding surface for the aeroshell extender piece.
[0048] It will be understood that the wind turbine blade may comprise a shaped or curved
surface, wherein the profile wedges are shaped to correspond to said shaped or curved
surface.
[0049] Where the extender piece is attached to a substantially cylindrical blade extender,
preferably the profile wedges comprise a first planar surface to attach to the extender
piece and a second concavely-curved surface to attach to the blade extender.
[0050] There is further provided a wind turbine comprising a wind turbine blade or wind
turbine blade assembly as described in any of the above embodiments.
[0051] There is further provided a method of assembly of a wind turbine blade portion having
a trailing edge extension, the method comprises the steps of:
providing a wind turbine blade portion having a leading edge side and a trailing edge
side;
providing a pressure-side panel of an aeroshell extension piece;
providing a suction-side panel of an aeroshell extension piece;
attaching a first profile wedge to a first side of said wind turbine blade portion;
attaching a first of said pressure- and suction-side panels to said wind turbine blade
portion at least partly using said first profile wedge;
attaching a second profile wedge to a second side of said wind turbine blade portion;
and
attaching a second of said pressure- and suction-side panels to said wind turbine
blade portion at least partly using said second profile wedge, wherein said pressure-
and suction-side panels form an aeroshell trailing edge extension for said wind turbine
blade portion.
[0052] Preferably, the method further comprises the step of attaching reinforcing elements
to said first of said panels, preferably said reinforcing elements comprise bulkhead
panels.
[0053] Preferably, said step of attaching a second of said pressure- and suction-side panels
comprises attaching said second panel to said reinforcing elements.
[0054] Preferably, the method further comprises the step of cutting said aeroshell trailing
edge extension from a trailing edge end to a point located towards said wind turbine
blade portion.
[0055] Although not part of the invention, there is also provided a method of manufacturing
an aeroshell extender piece for a portion of a profile of a wind turbine blade, the
method comprising the steps of:
providing a consolidated aeroshell extender piece for attachment to a trailing edge
of a portion of a wind turbine blade, preferably an inboard part of the wind turbine
blade, the extender piece having a first end for attachment to the trailing edge of
said profile, and a second trailing edge end to form an extended airfoil trailing
edge profile for the portion of the profile of the wind turbine blade; and
providing a plurality of slits in said consolidated aeroshell extender piece, each
of said plurality of slits extending from said second trailing edge end to a point
located towards said first end.
[0056] Preferably, said step of providing slits comprises performing cuts in said consolidated
extender piece from said trailing edge end towards said first end.
[0057] Preferably, the step of providing a consolidated extender piece comprises forming
an extender body through an infusion moulding process.
[0058] Preferably, said slits are formed wherein the dimensions of the slits do not significantly
impact aerodynamic performance in the area of the aeroshell extender piece. The slits
are arranged to be aerodynamically insignificant for the normal operation of the wind
turbine blade. It will be understood that aerodynamically insignificant is to be held
to mean that the dimensions of the slits are small relative to what would be required
to affect the aerodynamic performance of the wind turbine blade profile, e.g. in respect
of noise, lift/drag, etc.
[0059] In a first aspect, the step of performing cuts is configured wherein the width of
each slit formed by the cutting is less than boundary layer height in the area of
each slit. In a second aspect, the width of each slit is less than height of laminar
sublayer in the area of each slit, preferably at the design point of the wind turbine
blade.
[0060] Preferably, the step of performing cuts is configured wherein the slits have a gap
between opposed edges of the slit of less than 50 mm, preferably less than 25 mm.
In one embodiment, the slits have a gap width of approximately 15mm.
[0061] Preferably, the method comprises the step of arranging a flexible material in or
over the gaps defined by said plurality of slits, and/or brushes or bristles provided
at the gaps defined by said plurality of slits. The flexible material and/or brushes
or bristles may comprise any suitable material which is operable to cover or seal
the gaps without significantly affecting the structural properties of the aeroshell
extender piece, e.g. rubber, a flexible plastics material, canvas, etc.
[0062] Preferably, the step of performing cuts is arranged wherein said plurality of slits
are made along at least 50% of depth or chordwise length of the consolidated extender
piece from the trailing edge end towards the first end, preferably between 50-90%
of the depth of consolidated extender piece from the trailing edge end towards the
first end, preferably approximately 80% of the depth of the consolidated extender
piece from the trailing edge end towards the first end.
[0063] Preferably, the step of performing cuts comprises forming, preferably drilling, at
least one aperture in said consolidated extender piece, preferably a substantially
circular aperture, and cutting the body of said consolidated extender piece from the
trailing edge end to said at least one aperture.
[0064] Alternatively, the step of forming at least one aperture may be done when the consolidated
extender piece is manufactured, e.g. through the use of inserts during a moulding
process.
[0065] Preferably, the method comprises the step of providing a flexible material and/or
brushes or bristles on or over said at least one aperture.
[0066] Preferably, the step of performing cuts or slits is configured wherein the slits
on the body of the aeroshell extender piece are spaced from each other along the spanwise
length of the extender piece.
[0067] Preferably, the slits are spaced with approximately 1-5 metres between adjacent slits,
further preferably approximately 2-3 metres between adjacent slits.
[0068] Preferably, the step of providing a consolidated aeroshell extender piece comprises:
providing a pressure-side panel and providing a suction-side panel, the panels forming
a body;
providing reinforcing elements internal of the body of the aeroshell extender piece,
the reinforcing elements extending between opposed pressure- and suction-side panels.
[0069] Preferably, the reinforcing elements comprise bulkhead elements.
[0070] Preferably the steps of providing pressure-side and suction-side panels comprises
providing sandwich panels.
[0071] Preferably, the aeroshell extender piece is attached to the wind turbine blade profile
at least partly using profile wedges, wherein said profile wedges are shaped to provide
substantially planar bonding surfaces for the aeroshell extender piece. The profile
wedges are preferably provided as longitudinally extending pieces having a substantially
wedge shaped cross-section.
[0072] It will be understood that the wind turbine blade profile comprises a shaped or curved
surface, wherein said profile wedges are shaped to correspond to said shaped or curved
surface.
[0073] Preferably, the wind turbine blade profile comprises a substantially cylindrical
blade extender. In this case, the profile wedges preferably comprise a planar surface
to attach to said extender piece and a concavely-curved surface to attach to a surface
of said cylindrical blade extender.
[0074] Although not part of the invention, there is further provided a method of manufacturing
an aeroshell extender piece for a portion of a profile of a wind turbine blade, the
method comprising the steps of:
providing a pressure-side panel;
providing a suction-side panel;
attaching a plurality of reinforcing elements to a first of said pressure- and suction-side
panels; and
attaching a second of said pressure- and suction-side panels to said plurality of
reinforcing elements and to said first panel to form a consolidated aeroshell extender
piece.
[0075] Preferably, the consolidated aeroshell extender piece comprises a first end to be
attached to a portion of a wind turbine blade and a second trailing edge end to form
an extended airfoil trailing edge profile for the portion of the profile of the wind
turbine blade, wherein the method comprises the step of cutting said consolidated
aeroshell extender piece from said second trailing edge end to a point located towards
said first end to provide a plurality of slits in the body of the aeroshell to form
a flexible aeroshell extender piece.
[0076] Preferably, said plurality of reinforcing elements comprise bulkhead panels.
Description of the Invention
[0077] Embodiments of the invention will now be described, by way of example only, with
reference to the accompanying drawings, in which:
Fig. 1 shows a wind turbine;
Fig. 2 shows a schematic view of a wind turbine blade according to the invention;
Fig. 3 shows a schematic view of an airfoil profile of the blade of Fig. 2;
Fig. 4 shows a schematic view of the wind turbine blade of Fig. 2, seen from above
and from the side;
Figs. 5-8 illustrates a isometric perspective view of a series of step for a method
of manufacturing a flexible aeroshell extender piece according to an aspect of the
invention;
Fig. 9 illustrates a cross-sectional view of a wind turbine blade portion having an
aeroshell extender piece according to the invention; and
Fig. 10 illustrates a cross-sectional view of a profile wedge according to the invention.
[0078] It will be understood that elements common to the different embodiments of the invention
have been provided with the same reference numerals in the drawings.
[0079] Fig. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called
"Danish concept" with a tower 4, a nacelle 6 and a rotor with a substantially horizontal
rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from
the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest
from the hub 8. The rotor has a radius denoted R.
[0080] Fig. 2 shows a schematic view of a wind turbine blade 10. The wind turbine blade
10 has the shape of a conventional wind turbine blade and comprises a root region
30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub
and a transition region 32 between the root region 30 and the airfoil region 34. The
blade 10 comprises a leading edge 18 facing the direction of rotation of the blade
10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite
direction of the leading edge 18.
[0081] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal
blade shape with respect to generating lift, whereas the root region 30 due to structural
considerations has a substantially circular or elliptical cross-section, which for
instance makes it easier and safer to mount the blade 10 to the hub. The diameter
(or the chord) of the root region 30 is typically constant along the entire root area
30. The transition region 32 has a transitional profile 42 gradually changing from
the circular or elliptical shape 40 of the root region 30 to the airfoil profile 50
of the airfoil region 34. The chord length of the transition region 32 typically increases
substantially linearly with increasing distance
r from the hub.
[0082] The airfoil region 34 has an airfoil profile 50 with a chord extending between the
leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases
with increasing distance
r from the hub.
[0083] It should be noted that the chords of different sections of the blade normally do
not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent),
thus providing the chord plane with a correspondingly twisted and/or curved course,
this being most often the case in order to compensate for the local velocity of the
blade being dependent on the radius from the hub.
[0084] Fig. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind
turbine depicted with the various parameters, which are typically used to define the
geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and
a suction side 54, which during use - i.e. during rotation of the rotor - normally
face towards the windward (or upwind) side and the leeward (or downwind) side, respectively.
The airfoil 50 has a chord 60 with a chord length c extending between a leading edge
56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is
defined as the distance between the pressure side 52 and the suction side 54. The
thickness
t of the airfoil varies along the chord 60. The deviation from a symmetrical profile
is given by a camber line 62, which is a median line through the airfoil profile 50.
The median line can be found by drawing inscribed circles from the leading edge 56
to the trailing edge 58. The median line follows the centres of these inscribed circles
and the deviation or distance from the chord 60 is called the camber
f. The asymmetry can also be defined by use of parameters called the upper camber (or
suction side camber) and lower camber (or pressure side camber), which are defined
as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.
[0085] Airfoil profiles are often characterised by the following parameters: the chord length
c, the maximum camber
f, the position
df of the maximum camber
f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles
along the median camber line 62, the position
dt of the maximum thickness
t, and a nose radius (not shown). These parameters are typically defined as ratios to
the chord length c. Thus, a local relative blade thickness
t/
c is given as the ratio between the local maximum thickness
t and the local chord length
c. Further, the position
dp of the maximum pressure side camber may be used as a design parameter, and of course
also the position of the maximum suction side camber.
[0086] Fig. 4 shows some other geometric parameters of the blade. The blade has a total
blade length
L. As shown in Fig. 2, the root end is located at position
r = 0, and the tip end located at
r =
L. The shoulder 40 of the blade is located at a position
r =
Lw, and has a shoulder width
W, which equals the chord length at the shoulder 40. The diameter of the root is defined
as
D. Further, the blade is provided with a prebend, which is defined as
Δy, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.
[0087] The wind turbine blade 10 generally comprises a shell made of fibre-reinforced polymer,
and is typically made as a pressure side or upwind shell part 24 and a suction side
or downwind shell part 26 that are glued together along bond lines 28 extending along
the trailing edge 20 and the leading edge 18 of the blade 10. Wind turbine blades
are generally formed from fibre-reinforced plastics material, e.g. glass fibres and/or
carbon fibres which are arranged in a mould and cured with a resin to form a solid
structure. Modern wind turbine blades can often be in excess of 30 or 40 metres in
length, having blade root diameters of several metres. Wind turbine blades are generally
designed for relatively long lifetimes and to withstand considerable structural and
dynamic loading.
[0088] The wind turbine blade 10 comprises a flexible aeroshell extender piece attached
to a portion of the blade to provide for an adjusted aerodynamic profile of the portion
of the blade. The aeroshell extender piece is preferably used to provide an extended
trailing edge profile for the portion of the blade.
[0089] In a particularly advantageous embodiment, the wind turbine blade is formed as a
wind turbine blade assembly, comprising an outboard blade part and an inboard blade
part, the inboard blade part comprising a blade extender and an aeroshell extender
piece provided on the blade extender to form an extender trailing edge, for example,
as described in International Patent Application Publication No.
WO 2013/092852.
[0090] In Figs. 5-9, a method of manufacturing an aeroshell extender piece according to
an embodiment of the invention is illustrated.
[0091] With reference to Fig. 5, a cylindrical blade extender 70 or root end portion of
a blade is provided. The blade extender 70 may be formed from any suitable material,
e.g. a metallic extender formed from steel or another metal material, or an extender
formed as a fibre-composite structure, e.g. using glass- and/or carbon-fibres suspended
in a matrix of cured resin. It will be understood that, in alternative embodiments,
the blade extender may be provided as having an elliptical or asymmetric cross-sectional
profile.
[0092] A first extender panel 72 is provided to form a first external surface of an aeroshell
extender piece. The first panel 72 comprises an externally-facing surface 73a which
is used to form a portion of the external surface of the extended trailing edge of
the aeroshell extender piece, and an opposed internally-facing surface 73b.
[0093] With reference to Figs. 5 & 9, a first profile wedge 74 is provided for the attachment
of the first extender panel 72 to a surface of the cylindrical blade extender 70.
The first profile wedge 74 is used to present a suitable attachment surface, e.g.
an adhesive bonding surface, to allow for ease of attachment of the first extender
panel 72 to the blade extender 70. The first profile edge 74 may comprise an extended
body arranged to extend along the longitudinal direction of the blade extender 70
to which it is desired to attach an aeroshell extender, and/or the profile wedge 74
may comprise a plurality of wedge elements which are attached at locations along the
length of the extender 70.
[0094] The wedge 74 comprises a first shaped surface 75a for attachment of the wedge 74
to the surface of the blade extender 70, wherein the first shaped surface 75a is shaped
to correspond to the surface profile of the blade extender 70. For example, in the
embodiment of Fig. 5 the wedge 74 may comprise a singly curved surface 75a for attachment
to the curved surface of the cylindrical extender 70, but it will be understood that
the profile wedge 74 may comprise a doubly curved surface for attachment to the surface
of relatively more complex structures, e.g. a transition region of a wind turbine
blade. The wedge 74 further comprises a second planar surface 75b located opposite
to said first shaped surface 75a, wherein the wedge 74 is arranged such that the second
planar surface 75b presents a relatively flat planar surface, suitable for an adhesive
bonding surface.
[0095] The first shaped surface 75a of the profile wedge 74 is attached to the surface of
the blade extender 70, preferably using an adhesive bond, but any other suitable attachment
methods may be used, e.g. bolting, riveting, etc. Accordingly, the second surface
75b of the profile wedge 74 presents a bonding surface to which a first end 72a of
the first extender panel 72 can be attached, preferably using an adhesive bond, but
any other suitable attachment methods may be used, e.g. bolting, riveting, etc. Accordingly,
Fig. 5 presents a blade extender 70 having a first extender panel 72 of an aeroshell
extender piece attached via a first profile wedge 74, the first extender panel 72
attached to the profile wedge 74 at a first end 72a of the panel 72, with a second
trailing edge end 72b of the panel 72 projecting distal from the extender 70.
[0096] In Fig. 6, a second profile wedge 76 is attached at the opposite side of the blade
extender 70 to the first profile wedge 74. Similar to the first profile wedge 74,
the second profile edge 76 may comprise an extended body arranged to extend along
the longitudinal direction of the blade extender 70 to which it is desired to attach
an aeroshell extender, and/or the profile wedge 76 may comprise a plurality of wedge
elements which are attached at locations along the length of the extender 70.
[0097] With reference to Fig. 9, the second wedge 76 comprises a first shaped surface 77a
for attachment of the wedge 76 to the surface of the blade extender 70, wherein the
first shaped surface 77a is shaped to correspond to the surface profile of the blade
extender 70. For example, in the embodiment of Fig. 5 the wedge 76 may comprise a
singly curved surface 77a for attachment to the curved surface of the cylindrical
extender 72, but it will be understood that the second profile wedge 76 may comprise
a doubly curved surface for attachment to the surface of relatively more complex structures,
e.g. a transition region of a wind turbine blade. The wedge 76 further comprises a
second planar surface 77b located opposite to said first shaped surface 77a, wherein
the wedge 76 is arranged such that the second planar surface 77b presents a relatively
flat planar surface, suitable for an adhesive bonding surface. The first shaped surface
77a of the profile wedge 76 is attached to the surface of the blade extender 70, preferably
using an adhesive bond, but any other suitable attachment methods may be used, e.g.
bolting, riveting, etc.
[0098] A plurality of reinforcing elements 78 are provided which are to be attached to the
internally-facing surface 73b of the first panel 72 and which also may be attached
to the surface of the blade extender 72. The reinforcing elements 78 of Fig. 6 are
provided as planar panel elements, preferably bulkhead elements. The reinforcing elements
78 may be formed as sandwich panel constructions, e.g. having a core material such
as balsa or a low-density foam having an external skin layer, but it will be understood
that the reinforcing elements 78 may additionally or alternatively be provided in
alternate forms, e.g. as an internal truss structure, tension cables, metal plates,
etc. The reinforcing elements 78 may be attached to the first panel 72 and/or to the
blade extender 70 suing any suitable attachment method, preferably adhesive bonding.
[0099] With reference to Fig. 7, a second extender panel 80 is provided to form a second
external surface of an aeroshell extender piece. The second panel 80 comprises an
externally-facing surface 81a which is used to form a portion of the external surface
of the extended trailing edge of the aeroshell extender piece, and an opposed internally-facing
surface 81b.
[0100] The second extender panel 80 is attached to the assembly by securing a first end
80a of the second panel 80 to the second surface 77b of the profile wedge 76, preferably
by an adhesive bond. Accordingly, a second end 80b of the second extender panel 80
is arranged to form a trailing edge end of the second external surface of the aeroshell
extender piece.
[0101] While it will be understood that the first and second panels 72,80 may be arranged
such that the second trailing edge ends 72b,80b meet to form a relatively sharp trailing
edge of the aeroshell extender piece, in the embodiment shown in Fig. 7 the aeroshell
extender piece presents a blunt trailing edge 82, wherein a trailing edge panel 84
extends between the second trailing edge end 72b of the first extender panel 72 and
the second trailing edge end 80b of the second extender panel 80. It will be understood
that the trailing edge panel 84 may be provided as a separate component for attachment
to the second trailing edge ends 72b,80b of the first and second panels 72,80, and/or
for attachment to the plurality of reinforcing elements 78 at the trailing-edge-side
82 of the aeroshell extender piece. It will also be understood that the trailing edge
panel 84 may be formed integrally with one of the first and second panels 72,80, and/or
the trailing edge panel 84 may be formed by a first panel section projecting from
the trailing edge end 72b of the first extender panel 72 and a second panel section
projecting from the trailing edge end 80b of the second extender panel 80.
[0102] Fig. 7 illustrates a blade extender 70 having a consolidated aeroshell extender piece
indicated at 86, the consolidated aeroshell extender piece 86 forming an extended
trailing edge profile for the blade extender 70. The consolidated aeroshell extender
piece 86 may be converted to a flexible aeroshell extender piece through providing
trailing edge slits or slots in the body of the consolidated aeroshell extender piece
86.
[0103] With reference to Fig. 8, a plurality of slits 88 are formed in the body of the consolidated
aeroshell extender piece 86, preferably by performing cuts into the aeroshell body,
in particular into the trailing edge panel 84 and the first and second extender panels
72,80 from the trailing edge 82 of the consolidated aeroshell extender piece 86. The
slits 88 extend from the trailing edge 82 of the consolidated aeroshell extender piece
86, and extend to a point 88a located towards the first ends 72a,80a of the first
and second panels 72,80 of the consolidated aeroshell extender piece 86. Additionally
or alternatively, the slits 88 may be performed by cutting from the end points 88a
of the slits 88 towards the trailing edge 82 of the consolidated aeroshell extender
piece 86.
[0104] Preferably, the plurality of slits 88 are spaced with approximately 1-5 metres between
adjacent slits 88, further preferably approximately 2-3 metres between adjacent slits
88.
[0105] By providing slits 88 in this manner at the trailing edge 82 of the consolidated
aeroshell 86, the trailing edge 82 of the aeroshell is effectively divided into separate
portions along the length of the aeroshell. Accordingly, a relatively flexible aeroshell
extender piece 90 is formed, as the slitted or slotted trailing edge allows for a
relative bending or flexing between separate portions of the trailing edge 82 without
introducing relatively large bending stresses along the trailing edge 82. The slits
88 can allow for the aeroshell to "open", or to "close", along the spanwise direction,
due to a concertina-like movement between separate sections of the aeroshell as a
result of the bending of the blade structure during wind turbine operation. As a result,
the flexible aeroshell extender piece 90 may be formed having less reinforcement requirements,
resulting in a relatively lighter and more flexible construction than in the prior
art, and which provides for relatively easy construction and assembly.
[0106] Preferably, the plurality of slits 88 are formed along at least 50% of the depth
or chordwise length of the body of the aeroshell extender piece 90 from said trailing
edge end 82 towards the first ends 72a,80a of the first and second panels 72,80 located
at the blade extender 70. Preferably, the slits 88 extend between 50-90% of the depth
of the body from said trailing edge end 82 towards said first ends 72a,80a, preferably
approximately 80% of the depth of the body.
[0107] By providing slits 88 which extend along a majority of the depth of the aeroshell
90, but less than 100% of the depth, accordingly a flexible aeroshell 90 is provided
which allows for trailing edge deformation and bending, and which is simultaneously
securely attached to the blade extender 70 or other wind turbine blade portion. It
also makes it possible to provide the aeroshell as a uniform piece, which is retrofitted
to the inboard part of the blade, which may provide an relative simple attachment
to the inboard part of the blade, while still providing a flexible solution alleviating
loads.
[0108] The slits 88 may be formed using any suitable cutting action, e.g. machining, drilling,
sawing, etc. Alternatively, it will be understood that the panels 70,80,84 may be
formed having slots or apertures pre-formed in the panels themselves, wherein such
slots or apertures are aligned during assembly of the aeroshell to collectively define
the plurality of slits 88.
[0109] Preferably, the slits 88 are formed such that the aperture defined between opposed
edges of the slits 88 is aerodynamically insignificant for the normal operation of
the wind turbine blade. It will be understood that the slits 88 are dimensioned such
that the aperture is small relative to the dimensions which would be required to affect
the aerodynamic performance of the wind turbine blade profile, e.g. in respect of
noise, lift/drag, etc.
[0110] In one advantageous aspect, it is found that the slits 88 are preferably dimensioned
such that the width of the apertures provided by the slits is less than the designed
boundary layer height in the area of the slits.
[0111] In a second advantageous aspect, the width of the apertures provided by the slits
is less than the height of the laminar sublayer or the viscous sublayer in the area
of the slits.
[0112] It will be understood that the dimensions of the slits 88 may vary along the longitudinal
extent of the flexible aeroshell 86, dependent on the predicted normal operating conditions
of the wind turbine blade along the length of the aeroshell. Preferably, the width
of the apertures provided by the slits is less than 50 mm, further preferably less
than 25 mm. In one embodiment, the slits have a gap width of approximately 15mm.
[0113] Additionally or alternatively, the aeroshell extender piece 90 may comprises a flexible
material (not shown) which is provided in or over the apertures or gaps defined by
the plurality of slits 88. The flexible material may comprise any suitable material
which is operable to cover or seal the apertures without significantly affecting the
structural properties of the aeroshell extender piece, e.g. rubber, a flexible plastics
material, canvas, etc. Additionally or alternatively, the aeroshell extender piece
90 may comprises brushes or bristles (not shown) provided at the gaps defined by the
plurality of slits 88. The use of bristles or brushes at the slits can act to cover
the gaps defined by the slits, and reduce any negative aerodynamic effects which may
result by the presence of the slits at the trailing edge.
[0114] A relatively large aperture, preferably a circular aperture, may be provided at the
end point 88a of each of the plurality of slits 88.
[0115] In one aspect, the end point apertures 88a may be formed in the panels 72,80 prior
to the cutting of the plurality of slits 88, such that the end point apertures 88a
provide an alignment point or visual indicator to an operator for the correct alignment
of the slits 88. Additionally or alternatively, the end point apertures 88a may provide
an access point for the introduction of a cutting device which can be used to cut
said slits 88 into the body of the consolidated aeroshell extender piece 86, by cutting
an aperture or slot from said end point aperture 88a to the trailing edge 82 of the
consolidated aeroshell extender piece 86. The end point apertures 88a may be formed
by a cutting or machining of the panels 72,80, and/or the apertures 88a may be formed
integral to the panels 72,80 during a manufacturing of the said panels 72,80.
[0116] In a preferred embodiment, the plurality of reinforcement elements 78 are arranged
within the interior of the aeroshell extender piece wherein a pair of reinforcement
elements 78 are positioned on either side of and closely adjacent to each of the plurality
of slits 88. Accordingly, each pair of reinforcement elements 78 may act to substantially
seal off each effective trailing edge section of the flexible aeroshell 90 either
side of the slits 88, to prevent ingress of debris, etc., into the interior of the
aeroshell 90. In addition, the reinforcement elements 78 can act to provide structural
strength to each effective trailing edge section.
[0117] While the first and/or second panels may be provided as substantially flat planar
panel, it will be understood that more complex shapes may be used. For example, the
panels 72,80 may be shaped to form a suitably curved pressure-side or suction-side
surface, for example by providing a panel having a relatively concave or convex external
surface. With reference to the cross-sectional view shown in Fig. 9, it can be seen
that the first panel 72 is provided to have a relatively concavely-shaped externally-facing
surface 73a, to form a portion of the pressure-side of the wind turbine blade aeroshell
extender. Similarly, the second panel 80 may be provided as a planar panel or with
a relatively small curvature to form a slightly convexly-shaped externally-facing
surface 81a, to form a portion of the suction-side of the wind turbine blade aeroshell
extender.
[0118] In addition, while the reinforcing elements 78 are preferably provided as bulkhead
elements to substantially seal sections of the aeroshell 90, the reinforcing elements
78 may be provided with apertures 92 defined therein, to allow for drainage, pressure
equalisation, etc., between opposite sides of the reinforcing elements 78.
[0119] It will be understood that the panels 72,80,84 and/or the reinforcing elements 78
may be formed as sandwich panel constructions, e.g. by the infusion of layers of a
fibre material as a skin provided around an internal core material, e.g. balsa and/or
low-density foam core material.
[0120] While the illustrated embodiments show the use of an aeroshell on a cylindrical blade
extender, it will be understood that the aeroshell may be used on any other portion
of a wind turbine blade, e.g. at the root end of a wind turbine blade, along a trailing
edge section of a wind turbine blade, etc. Furthermore, while the illustrated embodiments
show the manufacture and assembly of the aeroshell on a cylindrical blade extender,
it will be understood that the aeroshell may be manufactured separately to an existing
wind turbine blade component, the aeroshell configured to be subsequently retrofit
to an existing component, e.g. a wind turbine blade having an inboard cylindrical
part, e.g. having a circular, elliptical or oval cross-section.
[0121] In addition, while the illustrated embodiments show the use of additional profile
wedges 74,76 to compensate for differences in the bonding surfaces of the blade extender
70 and the aeroshell panels 72,70, it will be understood that such compensatory profile
wedges may be formed integrally with the portion of the wind turbine blade, e.g. the
blade extender, to which it is desired to attach an aeroshell extender. In principle,
it would also be possible to integrate the profile wedges in the aeroshell extender,
which would alleviate loads in the glue bond to the surface of said portion of the
wind turbine blade.
[0122] The manufacture and use of a flexible aeroshell extender piece blade as shown provides
for improved operation of a wind turbine blade having such a flexible aeroshell, which
is more able to resist operational bending forces along the blade trailing edge during
the lifetime of the blade.
[0123] While the invention has previously been described with reference to an extender piece
provided with integrated slits, it is clear that the profile wedges can be utilised
for all types of extender pieces in order to achieve a larger glue bonding surface.
Accordingly, the profile wedges may also be used for extender pieces without slits.
According to the invention, the profile wedges are preferably adapted for attachment
to an inboard part of the blade, where the curvature is relatively large (or in other
words the radius of curvature is relatively low).
[0124] The profile wedge 74 according to the invention is shown in more detail in Fig. 10.
The profile wedge 74 is attached to the blade extender 70. The profile wedge 74 comprises
an inner surface 97, which is attached to the blade extender 70, and an outer surface
98, for attachment of the body of the extender piece 90. The inner surface 97 has
an inner radius of curvature R
i, and the outer surface has an outer radius of curvature R
o. The profile wedge 74 is advantageously designed such that the outer radius of curvature
R
o is larger than the inner radius of curvature R
i. Further, the outer surface 98 may have a larger area than the inner surface 97.
Thereby, a more flat and larger bond surface may be provided for the attachment of
the aeroshell extender piece 90. For a truly flat outer bonding surface, the outer
radius of curvature R
o approaches infinity. The profile wedge 74 may be formed as a composite structure
having a core material 94, such as balsawood or foamed polymer, wrapped in a fibre-reinforcement
material 96, e.g. glassfibre reinforced polymer.
[0125] The invention is not limited to the embodiments described herein, and may be modified
or adapted without departing from the scope of the present invention.